National security adviser Michael Flynn privately discussed U.S. sanctions against Russia with that country’s ambassador to the United States during the month before President Trump took office, contrary to public assertions by Trump officials, current and former U.S. officials said.

Flynn’s communications with Russian Ambassador Sergey Kislyak were interpreted by some senior U.S. officials as an inappropriate and potentially illegal signal to the Kremlin that it could expect a reprieve from sanctions that were being imposed by the Obama administration in late December to punish Russia for its alleged interference in the 2016 election.

Flynn on Wednesday denied that he had discussed sanctions with Kislyak. Asked in an interview whether he had ever done so, he twice said, “No.”

On Thursday, Flynn, through his spokesman, backed away from the denial. The spokesman said Flynn “indicated that while he had no recollection of discussing sanctions, he couldn’t be certain that the topic never came up.”

Officials said this week that the FBI is continuing to examine Flynn’s communications with Kislyak. Several officials emphasized that while sanctions were discussed, they did not see evidence that Flynn had an intent to convey an explicit promise to take action after the inauguration.

(Peter Stevenson/The Washington Post)

Flynn’s contacts with the ambassador attracted attention within the Obama administration because of the timing. U.S. intelligence agencies were then concluding that Russia had waged a cyber campaign designed in part to help elect Trump; his senior adviser on national security matters was discussing the potential consequences for Moscow, officials said.

The talks were part of a series of contacts between Flynn and Kislyak that began before the Nov. 8 election and continued during the transition, officials said. In a recent interview, Kislyak confirmed that he had communicated with Flynn by text message, by phone and in person, but declined to say whether they had discussed sanctions.

The emerging details contradict public statements by incoming senior administration officials including Mike Pence, then the vice president-elect. They acknowledged only a handful of text messages and calls exchanged between Flynn and Kislyak late last year and denied that either ever raised the subject of sanctions.

“They did not discuss anything having to do with the United States’ decision to expel diplomats or impose censure against Russia,” Pence said in an interview with CBS News last month, noting that he had spoken with Flynn about the matter. Pence also made a more sweeping assertion, saying there had been no contact between members of Trump’s team and Russia during the campaign. To suggest otherwise, he said, “is to give credence to some of these bizarre rumors that have swirled around the candidacy.”

Neither of those assertions is consistent with the fuller account of Flynn’s contacts with Kislyak provided by officials who had access to reports from U.S. intelligence and law enforcement agencies that routinely monitor the communications of Russian diplomats. Nine current and former officials, who were in senior positions at multiple agencies at the time of the calls, spoke on the condition of anonymity to discuss intelligence matters.

All of those officials said ­Flynn’s references to the election-related sanctions were explicit. Two of those officials went further, saying that Flynn urged Russia not to overreact to the penalties being imposed by President Barack Obama, making clear that the two sides would be in position to review the matter after Trump was sworn in as president.

“Kislyak was left with the impression that the sanctions would be revisited at a later time,” said a former official.

A third official put it more bluntly, saying that either Flynn had misled Pence or that Pence misspoke. An administration official stressed that Pence made his comments based on his conversation with Flynn. The sanctions in question have so far remained in place.

The nature of Flynn’s pre-inauguration message to Kislyak triggered debate among officials in the Obama administration and intelligence agencies over whether Flynn had violated a law against unauthorized citizens interfering in U.S. disputes with foreign governments, according to officials familiar with that debate. Those officials were already alarmed by what they saw as a Russian assault on the U.S. election.

U.S. officials said that seeking to build such a case against Flynn would be daunting. The law against U.S. citizens interfering in foreign diplomacy, known as the Logan Act, stems from a 1799 statute that has never been prosecuted. As a result, there is no case history to help guide authorities on when to proceed or how to secure a conviction.

Officials also cited political sensitivities. Prominent Americans in and out of government are so frequently in communication with foreign officials that singling out one individual — particularly one poised for a top White House job — would invite charges of political persecution.

Former U.S. officials also said aggressive enforcement would probably discourage appropriate contact. Michael McFaul, who served as U.S. ambassador to Russia during the Obama administration, said that he was in Moscow meeting with officials in the weeks leading up to Obama’s 2008 election win.

“As a former diplomat and U.S. government official, one needs to be able to have contact with foreigners to do one’s job,” McFaul said. McFaul, a Russia scholar, said he was careful never to signal pending policy changes before Obama took office.

On Wednesday, Flynn said that he first met Kislyak in 2013 when Flynn was director of the Defense Intelligence Agency and made a trip to Moscow. Kislyak helped coordinate that trip, Flynn said.

Flynn said that he spoke to Kislyak on a range of subjects in late December, including arranging a call between Russian President Vladi­mir Putin and Trump after the inauguration and expressing his condolences after Russia’s ambassador to Turkey was assassinated. “I called to say I couldn’t believe the murder of their ambassador,” Flynn said. Asked whether there was any mention of sanctions in his communications with Kislyak, Flynn said, “No.”

Kislyak characterized his conversations with Flynn as benign during a brief interview at a conference this month. “It’s something all diplomats do,” he said.

Kislyak said that he had been in contact with Flynn since before the election, but declined to answer questions about the subjects they discussed. Kislyak is known for his assiduous cultivation of high-level officials in Washington and was seated in the front row of then-GOP candidate Trump’s first major foreign policy speech in April of last year. The ambassador would not discuss the origin of his relationship with Flynn.

In his CBS interview, Pence said that Flynn had “been in touch with diplomatic leaders, security leaders in some 30 countries. That’s exactly what the incoming national security adviser should do.”

Official concern about Flynn’s interactions with Kislyak was heightened when Putin declared on Dec. 30 that Moscow would not retaliate after the Obama administration announced a day earlier the expulsion of 35 suspected Russian spies and the forced closure of Russian-owned compounds in Maryland and New York.

Instead, Putin said he would focus on “the restoration of ­Russia-United States relations” after Obama left office, and put off considering any retaliatory measures until Moscow had a chance to evaluate Trump’s policies.

Trump responded with effusive praise for Putin. “Great move on the delay,” he said in a posting to his Twitter account. “I always knew he was very smart.”

Putin’s reaction cut against a long practice of reciprocation on diplomatic expulsions, and came after his foreign minister had vowed that there would be reprisals against the United States.

Putin’s muted response — which took White House officials by surprise — raised some officials’ suspicions that Moscow may have been promised a reprieve, and triggered a search by U.S. spy agencies for clues.

“Something happened in those 24 hours” between Obama’s announcement and Putin’s response, a former senior U.S. official said. Officials began poring over intelligence reports, intercepted communications and diplomatic cables, and saw evidence that Flynn and Kislyak had communicated by text and telephone around the time of the announcement.

Trump transition officials acknowledged those contacts weeks later after they were reported in The Washington Post but denied that sanctions were discussed. Trump press secretary Sean Spicer said Jan. 13 that Flynn had “reached out to” the Russian ambassador on Christmas Day to extend holiday greetings. On Dec. 28, as word of the Obama sanctions spread, Kislyak sent a message to Flynn requesting a call. “Flynn took that call,” Spicer said, adding that it “centered on the logistics of setting up a call with the president of Russia and [Trump] after the election.”

Other officials were categorical. “I can tell you that during his call, sanctions were not discussed whatsoever,” a senior transition official told The Post at the time. When Pence faced questions on television that weekend, he said “those conversations that happened to occur around the time that the United States took action to expel diplomats had nothing whatsoever to do with those sanctions.”

In an earlier interview with The Post, Flynn acknowledged that he had been paid through his speakers bureau to give a speech at the event and defended his attendance by saying he saw no distinction between RT and U.S. news channels, including CNN.

A retired U.S. Army lieutenant general, Flynn served multiple deployments to Iraq and Afghanistan in the years after the Sept. 11, 2001, attacks — tours in which he held a series of high-level intelligence assignments working with U.S. Special Operations forces hunting al-Qaeda operatives and Islamist militants.

Former colleagues said that narrow focus led Flynn to see the threat posed by Islamist groups as overwhelming other security concerns, including Russia’s renewed aggression. Instead, Flynn came to see America’s long-standing adversary as a potential ally against terrorist groups, and himself as being in a unique position to forge closer ties after traveling to Moscow in 2013 while serving as director of the Defense Intelligence Agency.

Flynn has frequently boasted that he was the first DIA director to be invited into the headquarters of Russia’s military intelligence directorate, known as the GRU, although at least one of his predecessors was granted similar access. “Flynn thought he developed some rapport with the GRU chief,” a former senior U.S. military official said.

U.S. intelligence agencies say they have tied the GRU to Russia’s theft of troves of email messages from Democratic Party computer networks and accuse Moscow of then delivering those materials to the anti-secrecy group WikiLeaks, which published them in phases during the campaign to hurt Hillary Clinton, Trump’s Democratic rival.

Flynn was pushed out of the DIA job in 2014 amid concerns about his management of the sprawling agency. He became a fierce critic of the Obama administration before joining the Trump campaign last year.